1. Field of the Invention
This disclosure directs itself to an aiming and alignment system for a shell firing weapon and a method for aiming and aligning a shell firing weapon. In particular, this disclosure directs itself to a system that includes a portable aiming unit that is positionable in close proximity to the weapon and provides a relative special reference for use in aiming the weapon. Further, this disclosure directs itself to an aiming and alignment system that includes a sighting unit releasably mounted to the weapon that is adapted along with the portable aiming unit to establish at least one energy beam therebetween for defining a relative reference for aiming the weapon. Still further, this disclosure directs itself to a system where at least one low energy infrared emitter is used to provide an energy beam between the portable aiming unit and the sighting unit and periodically operated to track any displacement of the weapon during it's use.
2. Prior Art
Alignment systems for shell firing weapons are known in the art. Such systems typically include a sight unit mounted on the gun tube of the weapon, and aligned with it in such a manner that physical set knobs may be adjusted to achieve known, calibrated offsets between the tube and the optical sight. Absolute elevation of the tube is typically determined by observation of a bubble-level on the sight. Leveling of the bubbles by knob adjustment aligns certain tic-marks on the adjustment caliper system which may be read to determine elevation angle of the gun. Azimuth is typically obtained relative to a fixed external reference, such as a pair of poles, referred to as aiming posts, driven into the ground 50 and 100 meters from the weapon. The optical sight unit is arranged so that a telescope portion angles 45 degrees to the left of the true gun azimuth to sight on the posts.
To use such posts, the weapon is first hand set on the ground and aligned to a known absolute reference angle by compass, or, preferably by orientation of the sight unit telescope on a established field reference called an aiming circle. Arithmetic is required on the part of the gunner to adjust the lay of the gun according to the geometry of the configuration and the information obtained. The aiming poles are then placed by one crew member sighting through the sight unit telescope while a second crew member goes into the field and manually adjusts post positions until they are centered in the site reticle and directly behind each other from the gunner's point of view. Once set, azimuth angles are thereafter measured as a deviation from this reference point.
Larger field artillery have similar issues. Although the guns are typically vehicle or trailer mounted, the system still relies on a hand lay of the angle of the vehicle or trailer. In general, for artillery the aiming posts are replaced with an optical collimator that can be placed behind the guns and at a much closer distance.
Monitoring of hand laid weapon gun tube orientation presents many inherent difficulties. Supported by earth, they are mechanically independent of all primary aiming systems. Elevation tracking typically relies on bubble level type systems, while azimuth is typically referenced to aiming poles set out at a significant distance from the gun. Gun lay is a precision exercise in geometry and subject to human errors. Aiming poles require careful teamwork to place, and setting them at a sufficient distance can be problematic depending on firing position and potential for exposure to enemy fire. Once set, the guns are subject to extreme shock loading during operation, requiring round by round checks and adjustment. Each check requires that the gunner place his eye at the sight unit, judge the situation and make precision adjustment. Fatigue raises the probability of human error. With no means to directly measure round departure angles, the Fire Direction Center relies entirely on the gunner's acumen in maintaining the specified orientations as well as discovering and reporting errors.
The following considerations must be taken into account in developing a solution to the many limitations of the prior art.                1. An accurate solution must rely on at least one system component being physically isolated from the gun in order to provide a static reference that is immune to firing disturbances.        2. Placement for this component should preferably be along the standard 45° degree aiming post line. This prevents interference with established gun crew practices, minimizes safety hazards, and facilitates setup in a manner that is consistent with current training. It also minimizes sensor risk as it is known that these weapons shift, move earth, and occasionally even collapse forward due to failure of the weapon's bipod.        3. Placement of the static reference component at a short distance from the gun enables much faster setup and relaying times; however, placement as an modification to existing aiming post lights is an option. For larger artillery, upgrading the optical collimator to include systems disclosed herein is an option as well.        4. The electronic system should not interfere with traditional aiming methods, so that any new system can be transitioned into the field using existing weapon gun tubes and provide fall-back redundancy.        5. Concentrating additional technical components in the stand-off reference is preferable in order to minimize the need to modify the deployed weapon system, and minimize the need to engineer ultra-rugged components that can be mounted on the gun tube of the weapon.        6. The best placement for electronic guidance at the gun is the sight unit. A modified sight unit provides a very straightforward upgrade path to any currently deployed system, as well as maintaining a standard, reliable physical attachment point on the weapon's gun tube. Moreover, crews are already trained to remove the optical sight unit during early firing (before the gun is set) to avoid shock; similar treatment for digital components will similarly limit their exposure to excessive shock.        7. Low-energy IR has an excellent energy modality to use to link the stand-off reference component with the gun-mounted sight. By keeping the range between the components short, the system will be able to operate under similar dust and moisture conditions as those necessary to accommodate aiming poles, and with low enough energy emission to prevent the system from presenting any significant IR signature over and above the typical environmental background.        8. The system should be small, light-weight, and easily man-portable without adding significant new load to the current equipment roster.        9. Most guns have about 400 mils of range built into the gears or bipod. That means if the deflection needed is greater than 400 mils, the crew must pick up the gun and physically move it to meet the desired data. Any system that does not provide a 6400 mil capability (360 degrees) must provide for extremely rapid tear-down and setup so that it does not pose a burden for large changes in firing azimuth.        